MongoDB: Setting TTL on Documents

On some recent work I was doing with Winsitter, I needed an approach that would systematically remove documents after a specified period of time within MongoDB.

Previously, I would have written cron jobs or helpers to clean up the old data. No longer!

Come to discover, this feature already exists inside of MongoDB. It is called setting the TTL or Time to Live of a document.

The process involves creating an index on the date object you’d like to watch. In the example below, I am providing a property on my document called auditDate. I want the document associated with that property to automatically remove itself after 5 days or 432000000 miliseconds.

dbConnection.collection('audit').ensureIndex(
  {
    auditDate: 1,
  },
  {
    expireAfterSeconds: 432000000, // 5 days
  },
  function (indexErr) {
    if (indexErr) {
      console.log('error creating index');
      console.log(indexErr);
    }
  }
);

In the example, I’m using the MongoDB node.js library to ensure an index exists. If the index doesn’t exist, MongoDB will create it.

The expireAfterSeconds options tells MongoDB that after a specified amount of time, the document should automatically remove itself.

This quick fix has saved me a ton of time, and I am hoping it saves a ton for you too!

For more database tips, check out my guide on What is Dapper for efficient .NET data access.